The need for implementing electronic systems that are compatible with new additive manufacturing, 3D printing and direct-write processes has pushed current electronic manufacturing techniques to their limit. In particular, traditional approaches to the manufacture of printed circuit boards are not compatible with the needs of a new generation of electronic systems that call for electronic circuits to be conformal, flexible and hybrid in nature.
Conformal circuits are needed to place electronics in three-dimensional (3D) configurations rather than standard planar or 2D, a requirement that is becoming more urgent as 3D printed electronics mature and become more reliable. Flexible circuits require the integration of components into substrates or packages that are mechanically compliant so that they can conform, bend, stretch or fold to a level pre-designed without causing the circuit to fail. Finally, hybrid circuits are comprised of distinct discrete components integrated into single or multilayer architectures assembled on non-traditional substrates as opposed to printed circuit boards. Examples of such components include logic, communication, memory, sensing and power elements all integrated into a functional system or module.
The overarching challenge is to move away from traditional printed circuit fabrication techniques, which limit the ability to produce conformal, flexible and hybrid designs.
One of the most difficult obstacles toward this goal is to replace the way the interconnects on a circuit are currently generated using soldering of packaged components, which are bulky and of limited use in a conformal and/or flexible design, and wire-bonding of unpackaged devices (incompatible with the low profile requirements of most conformal and hybrid designs).
The solution to this problem calls for the development of processes and techniques that allow the printing of low profile, yet robust interconnects between discrete components.
To date, the use of printable inks or pastes to form interconnects has only had limited success due to the poor electrical performance of these printed filaments and their fragile nature.
Processing techniques such as laser direct-write (LDW) offer a viable alternative for the fabrication of low profile yet compliant, and robust, yet electrically conductive interconnects. These techniques allow the patterning of customizable electrically conductive metallic beams, which can be shaped or formed via laser folding to accommodate misalignment and strains between components. The same techniques then enable the non-contact laser-transfer of these shaped beams placing them precisely across the devices to electrically connect them across a gap. As a result, the ability to shape and print low profile, electrically conductive and free-standing interconnects across a gap for wiring the components required for the fabrication of conformal, flexible and hybrid electronics becomes possible for the first time through the application of this invention.
In order to create a suite of additive manufacturing processes capable of fabricating and assembling robust electronic circuits, this invention extends our previous work on the laser-induced forward transfer (LIFT) of discrete devices to include the transfer of metallic interconnects and commercial solder pastes.
In addition to applying LIFT to the laser transfer of solid metal interconnects, this invention incorporates the laser-induced bending and/or shaping of these interconnects in order to create structures that are capable of accommodating very large strains.
In conjunction with these two steps, a LIFT process is also used to print conductive adhesives or solder pastes, resulting in low-profile interconnects that are both mechanically and electrically attached to the device and surrounding circuit and are capable of withstanding deformation and strains that would result in the failure of a traditionally inkjet printed metallic trace.